The invention relates to a switch for receiving signals used in an electric equipment or electronic equipment such as an audio equipment, a video equipment, a communication equipment like a portable telephone, a measuring equipment and the like, particularly to an improvement of a movable dome-shaped contact spring which can be clicked.
A switch for use in a signal input part in the forgoing equipment conventionally comprises a dome-shaped contact spring which can be clicked, and a fixed contact part which faces a movable contact part disposed on an interior of the contact spring. A movable contact part having a hole has been recently frequently employed by the contact spring so as to prevent a loose contact between itself and the fixed contact part by a surface contact.
A contact spring is elastically deformed by a pressing force acting on a top thereof when a switch is operated, and a warping direction of the contact spring is reversed while it is clicked. When the warping direction of the contact spring is reversed, an edge part provided on the outer periphery of the hole of the movable contact part and the fixed contact part contact each other by a line contact so that they are rendered in an electrically on state, thereby generating signals in response to an object of the switch. A surface contact between the edge part of the movable contact part and the fixed contact part is substituted for a line contact therebetween so that a contact pressure at the edge part of the movable contact part is increased even if fine dust and the like exist, thereby making extensive improvements for an electric stability of contact between the movable contact part and the fixed contact part.
However, when a movable contact part is bored and a plate-like spring material is formed in a dome shape to manufacture a dome-shaped contact spring which can be clicked, the contact spring is not formed in a uniform dome shape because a spring member springs back after the contact spring was manufactured, and also the amount of movement or stroke serving as operating characteristics becomes large, and further a tensile stress or a compression stress imposed on the periphery of the hole becomes large when the contact spring is repetitively used, so that the periphery of the hole is prone to crack. Accordingly, there arises a problem of a short life of the contact spring. Particularly, since a contact spring has been small in size at present, this problem frequently occurs.
As a result, it is a first object of the invention to provide a dome-shaped contact spring which can be clicked, and is excellent in an electric stability of contact between a movable contact part and a fixed contact part of the contact spring without shortening a life of a contact spring when the contact spring is repetitively used.
The dome-shaped contact which can be clicked is used together with a printed circuit board in a portable telephone and the like. A conductive pattern on the printed circuit board for use in a switch normally forms, on the same plane, a contact segment corresponding to an outer periphery of the contact spring and a fixed contact part corresponding to a movable contact part at the inner central portion of the contact spring. The dome-shaped contact spring normally contacts the contact segment at its outer periphery, and is reversed when a switch is turned on so that the movable contact part is in pressure contact with the fixed contact part of the conductive pattern, thereby bringing both the contact segment and the fixed contact part of the conductive pattern into an electrical conduction with each other.
When a switch is turned on, namely when the contact spring is reversed, it is effective that the outer peripheral edge part of the dome-shaped contact spring is formed in a shape of skirt by a conical surface so as to ensure that the outer peripheral part of the contact spring is in pressure contact with the contact segment. Further, a skirt-shaped part is not reversed when the contact spring is reversed, and the outer peripheral edge part of the skirt-shaped part is in pressure contact with the contact segment.
Since the stroke of the contact spring is increased or decreased owing to the existence of a skirt-shaped part or depending on the manner of formation of the skirt-shaped part, and a load for reversing the contact spring becomes large and also a returning load for returning the contact spring becomes large when a pressing position is displaced from the central position of the contact part, there arises a problem that clicking feeling becomes worse at the position remote from the central position of the contact spring.
It is therefore a second object of the invention to ensure a stroke of the dome-shaped contact spring required for an eccentric load which is imposed on the dome shaped contact spring when it is pressed, thereby reducing variations in clicking feeling depending on the pressing positions.
To achieve the first object of the invention, a depression is formed on an inner central part of a dome-shaped contact spring which can be clicked, namely, on a movable contact part, and an edge part formed on the periphery of the depression is allowed to contact a surface of a fixed contact part by a line contact, thereby ensuring electric stability of contact between the edge part and fixed contact part, and also preventing a life of contact spring from being shortened without boring the movable contact part.
To achieve the second object of the invention, the central part of the dome-shaped contact spring which can be clicked is formed in a dome part by a spherical surface and an outer edge part of the dome part is formed in a skirt part by a part of one or not less than two conical surfaces, and also an annular demarcating part between the dome part and the skirt part is formed in a bent part, thereby ensuring a stroke of the contact spring which is required when the dome-shaped contact spring is pressed, and reducing variation in clicking feeling depending on the pressing positions.
More in detail, in a switch of the invention comprising the dome-shaped contact spring which can be clicked, the movable contact part formed at the inner central part of the contact spring contacts the fixed contact part or breaks off the contact with the fixed contact part so as to render the movable contact part and the fixed contact part to be in electrically on or off state, wherein a depression is formed on the movable contact part, and the edge part formed on the periphery of the depression is allowed to contact the surface of the fixed contact part (first aspect of the invention).
Further, the switch of the invention comprises, a switch case which houses therein a dome-shaped contact spring which can be clicked and an operation button which is brought into contact with a top of the contact spring and is freely displaced in a direction of the elastic deformation of the contact spring, wherein an outer periphery of the contact spring is brought into contact with the contact segment while the inner central portion of the contact spring serves as a movable contact part, and further the movable contact part contacts the fixed contact part or breaks off the contact with the fixed contact part inside the switch case, thereby rendering the movable contact part and the fixed contact part to be in electrically on or off state, wherein an edge part the switch further comprises a depression on the movable contact part, and the edge part formed on the periphery of the depression is allowed to contact the surface of the fixed contact part (second aspect of the invention).
The central portion of the dome-shaped contact spring which can be clicked is formed in a dome part by a spherical surface wherein the outer peripheral edge part of the dome part is formed to have a single or not less than double step by one or not less than two different conical surfaces, and the annular demarcating part between the dome part and the skirt part and the annular demarcating part between adjacent skirt parts are formed in bent parts (third and fourth aspects of the invention).
The depression of the movable contact part is formed in any of a circular, an elliptical, a polygonal and an astral shape.